I don't know for certain, BUT I was at a GameStop over the holiday weekend and looking through their accessories selection for the 360 in the search for a second play and charge cable. Didn't find that, but I did see a contraption that looks like it plugged into the proprietary AV connector, and all it had on it was composite and optical audio outputs. There were NO video outputs of any kind.
So, one could reasonably infer from that that the signal is sent to BOTH the proprietary AV connector port AND the HDMI port simultaneously. However, I can't guarantee this is the case.
It should be possible, however, to get an HDMI switch. If you look hard enough, you can find dual output devices. So one output could go to the TV, the other to a receiver or something for external speakers.
Okay I recently got an HDTV and I'm thinking about maybe hooking up some external speakers. My question is that I know HDMI carries audio to the television but if I have the audio adapter hooked up to the XBOX 360 will the console send 2 audio signal at the same time? One to go through the HDMI and the other through the adapter that will be hooked up to a receiver. Thanks for any answers.

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